This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No. 2001-082894 filed Mar. 22,2001.
1. Field of the Invention
The present invention relates to a fuel supply system for a dimethyl ether engine, wherein dimethyl ether is supplied to a high-pressure fuel pump from a fuel tank whilst being raised to a saturated vapour pressure or above by means of a pressure feed pump, and is then raised by this high-pressure fuel pump to a pressure suitable for injection into a combustion chamber of an engine and supplied to a common rail to which a fuel injection device is connected.
2. Description of the Related Art
As shown in FIG. 4, in a conventional fuel supply system for a dimethyl ether engine, an electromotive pressure feed pump 52 for dimethyl ether fuel supply is provided in a fuel tank 51, in such a manner that dimethyl ether is supplied to a high-pressure fuel pump 54 by the pressure feed pump 52, by means of a fuel pipe 53. The high-pressure fuel pump 54 is connected to a common fuel 56, to which a fuel injection device 55 is connected, and the dimethyl ether is supplied to the common rail 56 whilst being raised to a pressure suitable for injection into an engine.
Here, the high-pressure fuel pump 54 has a piston structure comprising a plunger, or the like, in such a manner that the pressure of the dimethyl ether is raised by reciprocal motion of this plunger.
In the fuel supply system for a dimethyl ether engine described above, the lubrication of the plunger and plunger barrel inside the high-pressure fuel pump 54 is performed by the dimethyl ether fuel which contains an added lubricating agent.
Therefore, if the dimethyl ether is not supplied to the high-pressure fuel pump 54 in a liquid state, then a problem arises in that the lubrication of the plunger inside the pump is not performed smoothly and scraping and burning of the plunger, and the like, arises.
In other words, in cases where the fuel is diesel oil, for example, then even if the supply of fuel is interrupted for a short period of time, the peripheral region of the plunger does not become dry rapidly, whereas in the case of dimethyl ether, since the fuel is a gas at normal temperature and normal pressure, the peripheral region of the plunger does become dry rapidly and hence the aforementioned problems are liable to occur readily. Such problems are particularly frequent when starting up the engine.
The present invention was devised in order to resolve the aforementioned problems, an object thereof being to provide a dimethyl ether fuel supply system capable of driving a high-pressure fuel pump, whilst ensuring internal lubrication of the high-pressure fuel pump.
In order to achieve the aforementioned object, a first aspect of the present invention is a fuel supply system for a dimethyl ether engine, wherein dimethyl ether is supplied from a fuel tank to a high-pressure fuel pump whilst being raised to a saturated vapour pressure or above by means of a pressure feed pump and is then raised to a pressure suitable for injecting into an engine by means of the high-pressure fuel pump and supplied to a common rail to which fuel injection devices are connected, comprising: a dimethyl ether detecting device, disposed in a fuel pipe leading to the high-pressure fuel pump, for detecting the state of the dimethyl ether from the pressure feed pump; and an electronic control unit, connected to the dimethyl ether detecting device, for driving the high-pressure fuel pump when the dimethyl ether inside the fuel pipe leading to the high-pressure fuel pump is in a liquid state.
According to the composition described above, since the state of the dimethyl ether inside the fuel pipe leading to the high-pressure fuel pump is detected by a dimethyl ether detecting device, and the high-pressure fuel pump is driven by an electronic control unit in accordance with the state of the dimethyl ether, the high-pressure fuel pump is driven, causing compression of the dimethyl ether, only in cases where dimethyl ether in a liquid state is being supplied to the high-pressure fuel pump and hence lubrication thereof is ensured, thereby making it possible to prevent sticking, burning, or the like, of the internal mechanism of the high-pressure fuel pump.
A second aspect of the present invention is a fuel supply system for a dimethyl ether engine according to the first aspect of the present invention, wherein the dimethyl ether detecting device consists of a temperature sensor for detecting the temperature of the dimethyl ether inside the fuel pipe leading to the aforementioned high-pressure fuel pump and a pressure sensor for detecting the pressure of the dimethyl ether.
A third aspect of the present invention is the fuel supply system for a dimethyl ether engine according to either claim 1 or claim 2, wherein the electronic control unit is connected to an engine key section, as well as being connected to the pressure feed pump, and it activates the pressure feed pump when the engine key is set to an engine ON position, and activates the high-pressure fuel pump when the engine key is set to a starter ON position, only in cases where it is detected by the dimethyl ether detecting device that the dimethyl ether inside the fuel pipe leading to the high-pressure fuel pump is in a liquid state.
A fourth aspect of the present invention is a fuel supply system for a dimethyl ether engine, wherein dimethyl ether is supplied from a fuel tank to a high-pressure fuel pump whilst being raised to a saturated vapour pressure or above by means of a pressure feed pump and is then raised to a pressure suitable for injecting into an engine by means of the high-pressure fuel pump and supplied to a common rail to which fuel injection devices are connected, comprising: an electronic control unit for activating the pressure feed pump when an engine key is set to an engine ON position, and activating the high-pressure fuel pump when the engine key is set to a starter ON position, after a prescribed period of time from the activation of the pressure feed pump.
A fifth aspect of the present invention is the fuel supply system for a dimethyl ether engine according to the fourth aspect of the present invention, wherein the electronic control unit adjusts and changes the prescribed period of time in accordance with the internal temperature of the engine.